Conventionally, a fine structure is made by an exposure method with a two-beam interference. The exposure method with the two-beam interference includes a step of causing two laser beams to cross each other at a predetermined angle, thereby generating an interference beam (interference fringes) that has a light-dark distribution (optical intensity distribution) with a pitch similar to or shorter than the wavelength of the laser beam, and a step of irradiating a substrate with the interference beam. The exposure method with the two-beam interference also includes a step of dividing a single beam, which is emitted from a light source having a strong coherent, such as a laser device, into two branch beams. The two branch beams are caused to interfere with each other. The exposure method with the two-beam interference does not use a fine mask, but is able to obtain a fine and periodical exposure illuminance distribution.
A method of manufacturing a fine structure with the exposure method with the two-beam interference is disclosed, for example, in Japanese Patent No. 4,894,899. The technology disclosed in Japanese Patent No. 4,894,899 includes a step of dividing a light beam from a laser light source into a 0 order light beam and ±1st order light beams by a diffraction beam splitter, a step of causing the ±1st order light beams to pass through the respective condenser lenses, the respective spatial filters, and the respective mirrors thereby directing the ±1st order light beams toward a substrate supported in a stage, a step of causing the ±1st order light beams to interfere with each other on the substrate, and a step of exposing a photosensitive film on the substrate. The stage is able to rotate. As the exposing process is performed twice, it is possible to obtain a fine structure that has a plurality of columns or cones arranged in a periodic fashion.
An exposure device that uses the exposure method with the two-beam interference is disclosed, for example, in Japanese Patent No. 4,514,317. The exposure device drives the stage in a stepwise manner, and performs the exposure process on the workpiece a plurality of times (i.e., performs the overlapping exposure) such that the exposure takes place in an overlapping manner. As a result, the exposure intensity distribution becomes flat (constant) in a certain area of the workpiece. When the exposure device performs the exposure process a plurality of times, the exposure device scans and controls the interference fringes in each exposure process such that the interference fringes overlap each other.